METABOLIC PROCESSES IN THE PLANT. 



271 



optimum temperature for normal respiration in Lnipinus seedling's 

 is situated at 40 C M and the maximum at 45 C. At a tempera- 

 ture beyond this the cells begin to die, and the production of 

 Carbon dioxide rapidly falls. 



If we first determine the intensity of respiration of 50 gr. of 

 Lupinus seedlings at 20 C., and then expose the material in the 

 respiratory vessel to a temperature of about 100 C. for some 

 time, and again determine the Carbon dioxide production, 

 we find that it has now completely ceased. Dead plants do not 

 respire. Respiration is a function of living protoplasm. The 

 plants must, of course, be protected from excessive loss of water 

 while at the high temperature. It is also advisable to mix some 

 Salicylic acid with the research material, after investigating its 

 normal respiration, in 

 order to prevent any sub- [ T 



sequent development of R 



bacteria. 



In experiments respect- 

 ing the direct influence 

 of light, we use for the 

 respiratory chamber a 

 vessel such as is depicted 

 in Fig. 100. These are 

 manufactured by Tittel & 

 Co., Geierstal bei Wallen- 

 dorf (Thuringia), and con- 

 sist of a glass flask with 

 parallel walls. The dia- 

 meter of the circular faces is 13 cm., the distance between 

 them about 20 mm. The spiral tube, Sch, is connected up air- 

 tight at the lower end of the vessel ; the larger opening at the top 

 receives the thermometer and the gas exit tube. The vessel is 

 suspended in water, contained in a zinc box 30 cm. high and 

 10 cm. wide, the front and back of which are made of glass. This 

 box is placed at a window with a south aspect, inclining a little 

 backwards. In front of it, i.e. towards the window, is placed a 

 large glass box, also tilted somewhat backwards, which contains 

 a concentrated filtered solution of alum. We employ for examina- 

 tion perfectly chlorophyll-free floral structures, roots, or fungi 

 (say in quantities of 25-40 gr.). In the experiments themselves 

 the same precautions are to be observed as have already been 



FIG. 100. Apparatus for investigating the in- 

 fluence of light on respiration. 



